The purpose of this project is to study immune responses in man and experimental animals to natural and experimental rickettsial infections. We conducted a serosurvey of a mini-epidemic of Q fever in personnel at the University of Colorado Medical Center and an outbreak of abortion in dairy goats in Idaho attributed to Coxiella burnetii. This past year we also studied the morphological changes of the Legionnaires' disease bacterium during growth in liquid culture media using scanning electron microscopy and investigated the use of acridine orange as a vital stain for Legionella pneumophila. Another study used the guinea pig as an experimental model to determine serologic variation in strains of L. pneumophila, previously differentiated and assigned to serogroups by direct immunofluorescence using conjugated immune rabbit sera. Serologic reactions were measured by enzyme-linked immunosorbent assay (ELISA) using soluble antigen and the microagglutination (MA) test using particulate antigen.